In communication systems, the duration of the call setup (or call setup delay) is a factor in the quality of service (QoS). For certain services, such as interactive games, emergency voice calls, or “push to talk” over cellular (PoC), which are sensitive to the call setup delay, the call setup delay can be too lengthy (usually 6 to 10 seconds).
A brief introduction of call setup in a UMTS system is first provided. The process of call set-up for user equipment (UE) is represented by FIG. 1, which incorporates several main functional entities, such as the UE, NodeB, radio network controller (RNC) and core network (CN). FIG. 1 also shows a user initiated PoC service in the domain of packet service (PS), while radio resource control (RRC) connection is built in the dedicated channel (DCH).
As to the original call in FIG. 1, call setup usually contains the following steps:
1) RRC connection setup;
2) Non-access stratum (NAS) signaling setup and NAS signaling interaction;
3) Radio access bearer (RAB) setup.
As to the terminal call in FIG. 2, call setup usually contains the following steps:
1) Paging;
2) RRC connection setup;
3) Non-access stratum (NAS) signaling setup and NAS signaling interaction;
4) Radio access bearer (RAB) setup.
The objective of RRC connection setup is to build the dedicated signaling connection between the UE and the UMTS Terrestrial Radio Access Network (UTRAN), containing several RNCs and NodeBs, as well as transferring the signaling between UE and UTRAN, or between UE and CN, with a use of the UU interface (i.e. the over-the-air interface between UE and NodeB).
Phase 1 in FIG. 1 depicts RRC connection setup. UE sends a RRC CONNECTION REQUEST through random access channel (RACH), that is, the uplink common transportation channel. Before the message is sent, layer 1 has to send a PRACH preamble for try-access. If access is successful, the RRC connection is sent to set up messages. After receiving the RRC CONNECTION REQUEST, RNC will decide whether to permit the access of UE. If so, RNC will relocate the related resources and configure NodeB. The configuration includes Radio Link (RL) connection, lub interface (the interface of RNC and NodeB) data transport bearer setup and lub interface Frame Protocol (FP) synchronization. After configuring NodeB, RNC starts to relocate the internal entities of RNC, such as the entities of Radio Link Control (RLC) and Medium Access Control (MAC). Then through the common transportation channel Forward Access Channel (FACH), RNC send RRC connection Setup messages. UE, after receiving this message, relocates RLC, MAC and Layer 1. Then L1 synchronization of the dedicated physical channel takes place. Through uplink DCH, UE sends RRC Connection Setup Complete messages to indicate that RRC connection setup is successfully finished. Protocol analysis and test illustrate that RRC connection setup delays mainly involve delays at the stages of random access process, RRC CONNECTION REQUEST, NodeB relocation process of RNC, RRC Connection Setup, L1 synchronization, and RRC Connection Setup Complete.
The objective of NAS signaling connection setup is to build signaling interaction between UE and CN. NAS signaling connection setup and signaling interaction are shown by Phase 2 in FIG. 1. NAS signaling involves Service Request for the original call, Paging Response for the terminal call, Signaling Connection Control Part (SCCP) at IU interface (the interface between RNC and CN), Authentication and Ciphering request, Security Mode setup, Temporary Mobile Subscriber Identity (TMSI) reassignment, Activate Packet Data Protocol (PDP) Request, etc. According to the protocol, Authentication and Ciphering in NAS signaling and TMSI reassignment are optional. However, the following will be focused on the compulsory parts. Note, what is illustrated in FIG. 1 is NAS signaling in the process of PS domain session setup. The Circuit Switched (CS) domain has different NAS signaling. But the CS domain and the PS domain are generally similar from the point of view of NAS setup delay. Protocol analysis and test illustrate that NAS signaling connection setup delays mainly involve delays at the stages of Service Request or Paging Response, SCCP connection setup, Security Mode setup, Activate PDP Context Request (for PS domain), Setup (for CS domain), etc.
After NAS signaling connection completion, RAB setup is under way as shown by phase 3 in FIG. 1. CN sends RAB Assignment Request to RNC, which, after receiving the request, undertakes the mapping from RAB to RB, and RL relocation, ALCAP setup and FP synchronization to NodeB. Then RNC sends RB Setup to UE, which, whereupon relocates RLC, MAC and Layer 1 of its local end and sends RB Setup Complete to RNC. RNC, after configuring RLC and MAC of its local end, sends RAB Assignment Response to notify CN of the successful setup of the side RAB. CN, as a matter of fact, will send Activate PDP Context Accept to UE, in order to inform UE that the data can be transmitted. Thus RAB setup is successful.
FIG. 2 shows the same signaling process from the point of view of the terminal UE receiving the call. As the figure shows, the process begins as the terminal UE receives a paging request from CN. The signaling process then continues just as described for FIG. 1, with the additional step that UE sends a paging response at the beginning of the NAS phase.
It is obvious that the call setup process of the present technique involves so many signaling steps that the call setup time delay is a little bit long. As shown by the data and tests, the call setup time delay of UMTS system is longer than that of the GSM system. Therefore, as to the service that is sensitive to the call setup delay, it is necessary to reduce the call setup time delay of UMTS system to improve the users' satisfaction.